The present invention relates to an apparatus and a method of casting metal articles in moulds having inlets at the side or bottom. The apparatus comprises
a) a supply unit for molten metal comprising a closed chamber capable of containing a mass of molten metal in its bottom region and a gas above the mass,
b) a filling tube extending from the bottom region upwardly to a connector for temporary connection to a filling duct in a mould for casting an article of metal,
c) means to vary the pressure in the gas between low values, at which metal from the mass when rising through the filling tube does not reach the connector, and higher values, at which molten metal is made to flow through the connector into the filling conduit in the mould.
When previously carrying out a method of the kind referred to above, difficulties have been encountered when adjusting the level of metal in the filling tube prior to the process of filling each mould with a view to achieving identical starting points for the filling of all moulds being filled successively. Previous attempts at determining the pressure corresponding to the datum level of the molten metal in the filling tube just prior to filling of each mould have not been very successful, because it has been based upon a computation of the difference in level between the connector to be connected to each mould and the level of the mass of metal contained in the supply unit. This computation is not particularly accurate, and is not made easier by the fact that the surface of the mass and metal in the supply unit is lowered upon each casting operation, possibly also reduced due to the limiting walls not being vertical or parallel.
From WO-A-89/07879 a die casting process of this kind is known. A sealed vessel with molten metal is via a filling tube temporarily connected to a mould and the molten metal is filled into the mould by a rising gas pressure in the vessel. A level indicator is provided in the filling tube to ensure equal starting level of the melt for each new mould to be filled.
It is the object of the present invention to provide an apparatus and a method of the kind referred to above, with which it is possible to ensure that each single process of casting in each of the successive moulds proceeds from the same starting point represented by the datum level referred to above, and this object is achieved by, according to the invention, proceeding in the manner set forth in detail hereinbelow. By so doing, the datum level is determined for each and every mould, independently of the level of metal in the reservoir in the supply unit.